1. Field of Invention
The present invention relates to a hydraulic brake and, more particularly, to a simple and reliable proportionally controllable hydraulic brake system.
2. Related Prior Art
A hydraulic brake system is essential for a car. For a car with four wheels, the hydraulic brake system generally includes a hydraulic pump for pumping brake fluid for example to four hydraulic cylinders each for driving a brake to slow down a related one of the wheels. Thus, a brake force is provided to each of the wheels from a related one of the brakes. The brake forces must be balanced to avoid any considerable difference between the brake forces on the right wheels and the brake forces on the left wheels that would otherwise cause the car to bias. Moreover, the braking forces must be kept below a limit to avoid lock of the wheels that would otherwise cause the car to skid.
Various devices have been devised to control the operation of the brake systems. For example, there are electric brake force distributors (“EBD”), traction control systems (“TCS”) and anti-lock brake systems (“ABS”). These devices are used to improve the efficiency and effectiveness of the operation of the brake systems to prevent bias or skid of cars.
Referring to FIG. 1, a conventional skid-proof hydraulic brake system 1 includes a body 10 with channels defined therein. The skid-proof hydraulic brake system 1 further includes two inlet valves 11, two outlet valves 12, an accumulator 13, a pilot valve 14, a reversible valve 15, a vacuum brake booster port 100 and a caliber port 102 on each of two halves of the body 10 divided by a midline C. The vacuum brake booster port 100 is used for connection to a vacuum brake booster (not shown). The caliber port 102 is used for connection to calibers (not shown).
The four inlet valves 11, four outlet valves 12, two pilot valves 14 and two reversible valves 15 are necessitated by various modes of hydraulic pressure provided by the TCS, ABS or EBD. Hence, the number of the elements of the skid-proof hydraulic brake system 1 is large. It is difficult and expensive to make the channels in the body 10. Moreover, it is difficult and expensive to connect the four inlet valves 11, four outlet valves 12, two pilot valves 14 and two reversible valves 15 to the body 10. The large number of the elements renders the skid-proof hydraulic brake system 1 bulky and unreliable.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.